Facebook has had numerous things — like concerns over mobile monetization and pre-IPO overhyping — contribute to the near-halving of its stock since its IPO, but anticipation of the lock-up expiration seems to be weighing on investors, as FB has shed more than 30% in the past month.

A lock-up expiration doesn’t necessarily guarantee there will be lots of selling — after all, many holders might be bullish on the long-term prospects of Facebook and wait things out.

But they often can be dark days for newly public companies. The most recent example is Angie’s List (NASDAQ:ANGI), which has struggled to stay above its first-day price of $16, and sunk 15% Tuesday to below its $13 IPO pricing after a ban on the sale of 25 million of its shares was lifted.

In Facebook’s case, a number of employees likely will be looking to snag some gains, if only to buy a house, a car, or some other big-ticket item. Others might just want to add some diversification to their portfolio.

VCs also might want to book some profits as well. Keep in mind that they often distribute the stock to their limited partners.

There’s also another wrinkle — the capital gains taxation rate could increase next year, so some Facebook holders might just want to play it safe and sell so they don’t miss out on more favorable tax treatment.

That said, if Thursday passes and all is well, Facebook still won’t be out of the woods. In addition to its numerous issues, the company also has other lock-ups expiring in October, November and December — and those total a massive 1.2 billion shares.

Based in Silicon Valley, Tom Taulli is in the heart of IPO land. On a regular basis, he talks with many of the top tech CEOs and founders trying to find the next hot deals and finding out which start-ups are stinkers.

A long-time follower of the IPO scene, back in 1999 Tom started one of the first sites in the space called WebIPO. It was a place where investors got research as well as access to deals for the dot-com boom. Tom also wrote the top-selling book, Investing in IPOs. In it, he covers all the aspects of analyzing an IPO, such as reading the prospectus, detecting the risk factors and understanding some of the arcane regulations. But don’t worry — if that process is too intimidating for you, thankfully Tom will do the legwork for you right here in the IPO Playbook blog.

Tom is routinely quoted in the media about upcoming deals with his interviews on CNBC and Bloomberg TV, but he is eager to take your questions too. You can message him on Twitter at @ttaulli. And feel free to weigh in via the comments section on any of his IPO Playbook posts.